Preparation of esters of polybasic acids



Patented Mar. 5 1935' UNITED STATES PATENT v OFFICE PREPARATION or nsrnns 0F ro'mznnsrc ACIDS Emmette F. Izard, Elsmere, DeL, assignor to E. du Pont de Nemours & Company, Wilmington,

- Del., a corporation of Delaware No Drawing. Application February 14, 193 3, I

Serial No. 656,766 1 17 Claims. (Gl. 260-103) p The present invention relates to a process for the preparation of polybasic acid esters and more.

particularly to the preparation of a mixture of diesters of the'di-basic acids from the lower alkyl esters thereof and higher oxygenated organic compounds.

Esters of the di-basic acids have been prepared from the anhydride of the acid and an alcohol. By reacting these compounds a monoester of the di-basic acid is obtained which is subsequently treated with a hydrogen halide and an alcohol to obtain the diester of the acid treated. Another method which is .usually suitable for the preparation of diesters of the di-basic acids consists in treating the di-basic acid and an alcohol in the presence of a suitable catalyst, such, for example, as benzene sulfonic acid; sulfuric acid, etc. When attempting to use such processes,

however, for the preparation of the esters of the polybasic acids from the higher oxygenated organic compounds obtained by the catalytic hydrogenation of carbon oxides undersupera-tmospheric pressure (many patents describe how these compounds may be prepared, e. g. 1,820,417 and 1,844,847), it has been found that the reactions ring and a considerable loss of .both the acid. and the oxygenated organic compound.

The charring and unsatisfactory yield obtained in attempting toproduce esters, by either of the above or other orthodox methods, from theoxy-. genated organic compounds referred to, may in part be due to the presence in the mixture of a large number of undetermined substances. It is known that the oxygenated organic compounds obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure are predominantly alcohols and after the lower ,alcohols have been removed there remains a mix-' ture of compounds hereinafter designated as higher oxygenated organiccompoundsf, which .include normal propanol, 'isobutanol, 2-methyl butanol-l, 3-methyl butano1-2, 2,.4-dimethyl pentanol-3-, 3-methyl pentano1-2, -methyl hexanol-l, and i-methyl heptanol-l, and higher alcohols.

In attempting to obtain the esters of the polybasic acids with these higher oxygenated organic compounds it has been found that only a portion thereof, presumably the primary alcohols, reacts to-form the ester. The compounds which readily react will be hereinafter designated as the reactive portion, while those compounds which do not react or whichreact with difliculty to form the ester will be designated as thenonnon-reactive portion involves, of course, a number of operative steps which considerably in w creases-the cost of the ester produced. Nevertheless, in spite of this separation, no decrease in amount of charred by-pr'oduct was obtained when the separated portions were esterified.

An object of the invention is to provide an improved process for the preparation of esters of the polybasic acids. Another object of the invention is to provide a process for the preparation of the esters of the polybasic acids'by the interaction'of the loweralkyl esters of said acids with the oxygenated organic compounds obtained by the catalytic hydrogenation of carbon oxide under superatmospheric pressure. A still-further object of the invention is to provide a process for the 25 preparation of the higher 'dialkyl phthalates by theinterchange of the lower alkyl groups of a phthalate for the higheralkyl groups derived from the oxygenated organic compoundsabove referred to. Another object is to provide suitable catalysts for this reaction. Other objects and advantages will hereinafter appear.

I have found that the poly-esters of the polybasic acids and more particularly the diesters of the -dibasic acids can be prepared from the higher oxygenated organic compounds without the-dim culties which are present when this esterification is effected by the orthodox methods above described, and, furthermore, without the necessity of separating the reactive portions of the compounds from the non-reactive portions. thereof. I have been able to effect this result by treating the mixture of reactive and non-reactive. portions with an already prepared lower alkyl ester of the polybasic acid, in the presence of a suitable catalyst. By this procedure many of the alkyl groups in the alcohols present in the mixture dieplace the alkyl groups from the ester of the polya lower alkyl ester of a polybasic acid, such, for example, as dimethyl phthalate. A suitable catalyst is added to the mixture and the whole refluxed and the alcohol displaced from the ester (methanol in the 'case of'dimethyl phthalate) is allowed to distill over. When the alkylgroup in the ester is no longer being displaced, the alcohol ceases to distill over and the reaction is substantially complete. The temperature of the reacted mixture is then raised and the non-reactive portions are separated by distillation, leaving in the reaction vessel the catalyst and the ester formed by the displacement of the alkyl radical in the polybasic acid by the reactive compounds of the higher oxygenated organic mixture. The catalyst is separated from the ester in any suitable manner, leaving the higher-ester of the polybasic acid. I

The higher oxygenated organic compounds which boil from approximately C. up may be separated by distillation into a number of fractions. In the higher boiling mixtures containing complex primary and secondary alcohols of widely varying reactivity, it has been found that by using the above procedure not all of the alcohols react to give the ester. For example, in the fraction boiling between Flo-190 C. only 45% react by the above ester interchange meth--' od when using dimethyl phthalate. A higher percentage, however, of the complex components in these fractions may be converted to the ester. This may be effected by treating the non-reactive portions of the oxygenated organic compounds, subsequent to their separation from the formed ester of the'polybasic acid, (i. e. the ester formed with the reactive portion) with a second addition of the lower alkyl ester of the polybasic acid. By this method the less reactive constituents will, in many instances, react with the lower alkyl ester of the polybasic acid to dis-' place generally one of the alkyl groups of the added ester. The resulting unsymmetrical ester after separation from the non-reactive portions of the mixture is then treated with a fresh portion of the higher oxygenated organic compounds, whereupon the polybasic acid will be converted to an ester in which has been substituted in one of the carportion, and in the v boxyl positions a less reactive other a reactive portion of the oxygenated oranic mixture.

In conducting my process I ordinarily use the methyl ester of the polybasic acid as the ester in which the alkyl group is displaced by thealkyl Other alkyl groups may, however,

groups from the higher oxygenated compounds. be used, such as the ethyl, propyl, and butyl esters. but in such instances, of course, if there be in the-oxygenated organic compounds alcohols of the same or a lesser number of carbon atoms than are present in the alkyl group initially present in the ester, no substitution or replacement by the loweralkyl groups from the alcohols will be eflected. The esters -of the following polybasic acids may be used: oxalic, malonic, succinic, phthalic, glutaric, adipic, pimelic, suberic, hexahydrophthalic, sebacic, carbonic, tricarballylic, aconitic, phosphoric, tartaric, etc.

It'has been indicatedabove that suitable catalysts may beemployed. Catalysts which are efllcient for esterification reactions generally are not, however, well adapted for my process, e; g. the use of acid catalysts such as sulfuric acid result in the formation of quantities of tar; while the unsymmetrical ester of ability, and ease of removal from the final product. p

I will now give several examples indicating preferred methods of conducting my process, but

it will be understood that I shall not be restrict-' ed by the details or proportions of the constituents indicated therein except as they may be limited in the appended claims.

Example 1.--A mixture of higher oxygenated organic compounds obtained by the catalytic hydrogenation of carbon oxides under elevated temperature and superatmospheric pressure was distilled over sodium, this mixture of compounds prior to purification boiling between -190 C. 2700 grams of the purified mixture was then thoroughly mixed with 840 grams of normal butyl phthalate and 30 grams of litharge. The resulting mixture was refluxed at a temperature of -195" C., the refluxing being conducted in such a manner that the butyl alcohol resulting from the displacementdistilled over. When 508 grams of normal butyl alcohol had been collected-in the condensate the temperature of the reacted mixture was increased until 1779 grams of theunreacted portion of the oxygenated organic compounds was collected in the condensate. The remaining product was filtered to remove theleadoxide catalyst with a resulting yield of 100,3 grams of the ester.

Example, 2.-A mixture of oxygenated organic compounds similar to that used in Example 1 is treated", after purificatio same manner as that given in cept. that dimethyl phthalate is used in lieu of dibutyl-phthalate. The unreacted portion. of the oxygenated organic compounds separated from the diester produced is further treated with a second portion of normal methyl phthalate, lead oxide being again used as the catalyst and the refluxing being carried same temperature. acid ester, which may be designated as methyl less-reactive-compound phthalate, is. obtained and is separated from the non-reactive portion of the oxygenated organic compounds. This unsymmetrical ester is then refluxed in the presence of a catalyst with a. fresh portion of the higher oxygenated organic compounds. r The resulting mixed esters contain alkyl groups from the less reactive constituents as well as alkyl groups from the more reactive constituents. The temperature of the reaction may beadvantageously decreased by the addition of carrier liquids such as toluene and the like.

It has been determined that the higher oxygenated organic compounds will likewise displace the lower alkyl groups present in esters of monobasic acids when the reaction is eifected in the manner similar to that described. Propionic,

Example 1, ex-

isobutyric, l-methyl pentanoic, 1-3 dimethyl pentanoic, thiocyanic, benzoic, phenyl acetic, etc. illustrate acids the esters of which may be so treated.

From a consideration of the above specification it will be realized that anyprocss effecting the adapted for this process as they' in substantially the out at approximately the' Anunsymmetrical phthalic preparation of esters of the polybasic acids from the higher oxygenated organic compounds obtained by the catalytic hydrogenation oi-carbon oxides under superatmospheric pressure will come withinthe scope of this invention, it the process is efiected in the manner hereinbeiore described or in any equivalent manner. I claim: 1. A process which comprises reacting a lower alkyl ester of a polybasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, to produce a mixture of esters of the acid.

.2. A process which comprises reacting a lower alkyl ester of a dibasic organic carboxylic acid with the higher oxygenated organic compounds,

obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, to produce a mixture of esters of the acid.

3. A process which comprises reacting dimethyl phthalate with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, to produce a mixture or esters or phthalic acid.

' 4. A process for producing a mixture of esters of the polybasic organic carboxylic acids which comprises interacting the higher oxygenated organic compounds, obtained from the catalytic hydrogenation of carbon oxides under superatmospheric pressure, with a lower alkyl ester of a polybasic organic acid, removing the alcohol formed by the displacement of the esterifying groups originally present in the ester, separating the non-reactive compounds from the ester which has been formed, and purifying the ester.

5. A process for the preparation of a mixture of esters of phthalic acid which comprises admixing the higher oxygenated organic compounds, obtained from the catalytic hydrogenation of carbon oxides under superatmospheric pressure, with a lower alkyl ester of phthalic acid, separating the unreactive compounds from the ester produced and finally purifying the ester.

6. A process for producing a mixture of esters of a normal polybasic organic carboxylic acid which comprises displacing the esterifying groups of the ester of a polybasic acid by the alkyl groups present in a mixture of higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmos pheric pressure. v

7. A process which comprises displacing the esterifying groups of the ester of a dibasic organic carboxylic acid with the alkyl groupsoi' the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxide under superatmospheric pressure, in order to produce a higher ester of the dibasic acid.

8. A process which comprises reacting a lower alkylester of a polybasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in the presence of a catalyst adapted toeflect ester interchange to produce a mixture of esters of the acid.

9. A process which comprises reacting a lower alkyl ester of a dibasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in the presence of a catalyst adapted to eflect ester interchange to produce -a mixture of esters oi the acid.

10. A process which comprises reacting a lower alkyl ester oi. a polybasic organic carboxylic acid with the higher oxygenated organic compounds, obtained'by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in the presence of a mildly alkaline catalyst adapted to efiect ester interchange to produce a mixture of esters of the acid.

- 11. A process which comprises reacting a lower alkyl ester of a dibasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in the presence of a mildly alkaline catalyst adapted to efl'ect ester interchange to produce a mixture of esters of the acid.

12. A process which comprises reacting a lower alkyl ester of a polybasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of car,- bon oxides under superatmospheric pressure, in the presence of a mildly alkaline catalyst selected from the group consisting of anoxide of lead, tin, cerium, zinc, calcium, aluminum, and silver, to produce a mixture of esters of the acid.

13, A process which comprises reacting a lower alkyl ester of a dibasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in

the presence of a mildly alkaline catalyst selected from the group consisting of an oxide of lead, tin, cerium, zinc, calcium, aluminum and silver, to produce a mixture of esters of the acid.

14. A process which comprises reacting a lower allwl ester of a polybasic organic carboxylic acid with the higher oxygenated organic compounds, obtained by the catalytic hydrogenationpf carbon oxides under superatmospheric pressure, in the presence of lead oxide as the catalyst to produce a mixture 01 esters of the acid.

15. A process which comprises reacting dimethyl phthalate with the higher oxygenated organic compounds, obtained 'by the catalytic hydrogenation of carbon oxides under superatmospheric pressure, in the presence of lead oxide as the catalyst to produce a mixture of esters of phthalic acid.

16. A process which comprises reacting dibutyl phthalate with the higher oxygenated organic compounds, obtained by the catalytic-hydrogenation or carbon oxides under superatmospheric pressure, in the presence of lead oxide as the catalyst to produce a mixture of esters of phthalic acid;

17. A process which comprises reacting dibutyl phthal'ate with the higher oxygenated organic compounds, obtained by the catalytic hydrogenation ot'carbon oxides under superatmospheric pressure; in the presence of litharge as the catalyst toproduce a mixture of esters of phthalic acid. I

EMME'I'I'E F. IZARD. 

